1. Field of the Invention
The present invention relates to a method for manufacturing an image sensor, and more particularly, to a method for manufacturing a CMOS image sensor which can maximize the color filter array effect of a CMOS image sensor and achieve simplification and stabilization of the process.
2. Description of the Related Art
Generally, a microlens is formed in order to maximize the effect of the color filter array (CFA) of a CMOS image sensor. Such a microlens is shaped by coating a photosensitive photoresist of silicon oxides based having high light transmittance by a spin-on coating machine, patterning the same by use of a mask, and curing the same by thermally flowing it.
FIG. 1 is a sectional view for showing a CMOS image sensor formed according to one of conventional techniques.
As shown in FIG. 1, a semiconductor device with a color filter and a microlens includes a semiconductor substrate 10 which has underwent shallow trench isolation (STI) and a passivation processes, a first overcoating layer (OCL) 12 formed on the semiconductor substrate 10, a color filter array (CFA) layer 14 formed on the overcoating layer 12, a second overcoating layer 16 and a microlens (ML) layer 18 formed on the second overcoating layer 16.
In case of forming a microlens with a size of less than 4 μm by the method as shown in FIG. 1, it is problematic in that the uniformity of size and height is lowered due to the inaccuracy of the boundary portions of the edges.
Moreover, it is difficult to measure a critical dimension (CD) due to the inaccuracy of a pattern, and the quantity of light approaching the photo-diode region is lowered due to the instability of the process.
Furthermore, it is difficult to adjust the thickness of a CFA and the CD size of the CFA due to the non-uniformity of the sub-topology upon forming of the CFA layer 14, thereby making the process unstable.
In a typical image sensor, the image of an object is stored in photo-electrons focused on the above-mentioned PD and then converted into an electric signal. Accordingly, the quantity of the image converted into an electric signal is decreased or becomes non-uniform, thus the image properties of the image sensor device are deteriorated and the sensor function is also deteriorated.
Further, although an etching process has been often employed in order to overcome the circumstance similar to the above-mentioned problem, this is such a process against the reduction of defects and this increases the number of process steps and becomes disadvantageous in terms of cost saving.